This disclosure relates to an ignition coil and a method for operating an ignition coil.
Ignition coils contain a transformer, with which a secondary voltage pulse for a spark plug is generated by feeding a primary voltage pulse. Usually, ignition coils also contain a control and monitoring unit that controls the transformer. The control and monitoring unit is usually connected to an engine control unit with which it communicates during operation. Ignition coils usually have a signal input and a signal output for this purpose.
This disclosure teaches how important operating information can be made available to an engine control unit with as little effort as possible during the operation of an ignition coil.
According to this disclosure, the primary current, the primary voltage, the secondary current and/or the secondary voltage are measured and monitored during operation of an ignition coil. If a malfunction is detected, an error signal is generated during a subsequent primary voltage pulse, the error signal indicating that a malfunction has occurred during the previous primary voltage pulse and classifying the malfunction. A malfunction can be determined by evaluating the course of the primary voltage, the secondary voltage, the primary current and/or the secondary current. For example, a malfunction can be detected by finding a deviation of the course of the primary current or the primary voltage or the secondary current or the secondary voltage from of an expected course or course range.
According to this disclosure, a possible malfunction to an engine control unit is therefore not reported in the same operating cycle of the ignition coil in which it occurs. Instead, the malfunction is communicated to the engine control unit only in the next operating cycle of the ignition coil, i.e., during the next primary voltage pulse. The monitoring can be simplified and realized with little hardware expense in this way.
The error signal may be a pulse, for example, a current pulse or a voltage pulse. The malfunction can be classified in this case, for example, by the duration of the pulse, its timing or its intensity, i.e., at a voltage pulse of its voltage level. The error signal can also be a pulse sequence, the pattern of which classifies the malfunction, that is to say is associated with a type of error or a combination of several errors.
The duration of the error signal can be used to classify the malfunction that has been ascertained by evaluating the course of the primary voltage or the secondary voltage. Possible malfunctions that can be classified are, for example, too long an activation of the coil, which is also referred to as overdwell, too rapid a decay of the secondary current, for example, due to a sliding discharge, too long a stopping of the secondary current, which for example can occur if the ignition voltage is too low or there is a short circuit, too high a temperature, or the occurrence of several of the above error cases at the same time. Thus, essential information about the error that has occurred can be transmitted by the error signal to the engine control unit without the need for additional transmission channels or data lines.
A further advantageous refinement of this disclosure provides that the error signal is generated on the same signal output on which a monitoring signal pulse is generated at least during some primary voltage pulses. The monitoring signal pulse is started as soon as the primary current reaches a first predetermined threshold value, and is terminated as soon as the primary current reaches a second predetermined threshold value that is greater than the first predetermined threshold. Thus, the signal output or the signal line connected to it can not only be used for transmitting an error signal, but also to communicate important information about the operation of the ignition coil to the engine control unit during regular operation, namely the speed at which the primary current increases. This information is important for the engine control unit in order to be able to precisely specify the desired ignition timing.
The monitoring signal pulse may be generated independently of the error signal, such that both an error signal and a monitoring signal pulse are generated during a primary voltage pulse. The error signal may then be sent before or after the monitoring signal pulse, sent both before and after the monitoring signal pulse, or even be integrated into the monitoring signal pulse, for example, its amount.
However, the monitoring signal pulse is preferably only generated if no malfunction has been determined during the preceding primary voltage pulse. When a malfunction occurs, such a monitoring signal pulse which communicates to the engine control unit how fast the primary current is increasing, is less significant. Therefore, upon occurrence of a malfunction in the subsequent cycle of the ignition coil, such a monitoring signal pulse can be dispensed with in favor of an error signal.
To facilitate distinguishing monitoring signal pulses and error signals, the error signal is preferably started and terminated before the primary current reaches the first threshold value. An error signal then occurs essentially earlier in the operating cycle of the ignition coil than a monitoring signal pulse. The engine control unit can thus recognize these different pulses by how early or how late they occur in an operating cycle of the ignition coil. Alternatively or additionally, error signals and monitoring signal pulses can basically also be distinguished on the basis of the pulse duration, since the time duration in which the primary current increases from the first predetermined threshold value to the second predetermined threshold value is not precisely known to the engine control unit, but this time period always lies in a defined and known range.